High tonnage rim press

ABSTRACT

A high tonnage reaction injection molding (RIM) press has fixed and movable platens for clamping a composite mold therebetween at a closed mold position. A plurality of high pressure hydraulic cylinders are mounted on a carrier for the movable platen, and a locking mechanism having a plurality of incrementally spaced locking positions is effective to lock the carrier selectively at said positions. A pair of low power hydraulic piston-cylinder assemblies connected with the carrier adjacent to its opposite ends move the carrier and movable platen to the closed position. Short stroke connecting rods operated by the high pressure cylinders are forced independently of each other into high tonnage engagement with the movable platen at a plurality of locations within the area of the composite mold to clamp the latter between the platens and positively seal its junctures, whereupon a RIM mix head injects the high pressure reactive chemicals into the sealed mold. 
     Sensor means including a pair of sensors associated with said pair of low power assemblies sense deviations of said opposite ends from a reference plane and cooperate with the associated low power assemblies to maintain the carrier at a predetermined attitude with respect to said plane as the carrier moves to said closed position. The sensor means also sense the distance that the carrier must be moved from the closed position to the next successive locking position, then in sequence, actuate said low pressure assemblies to move said carrier to said next successive locking position, thereby to provide space between said carrier and movable platen, actuate a spacer to span said space and prevent its closure during successive press operations, actuate said high pressure cylinders to clamp the mold between said platens, and finally actuate a RIM mix head to inject the high pressure reactive chemicals into said mold.

This application is a continuation-in-part of co-pending U.S.application Ser. No. 07/318,574, filed Mar. 3, 1989, now U.S. Pat. No.4,944,669, and is concerned with an improved press which, though notlimited to any specific size or use, is particularly suitable for thereaction injection molding (RIM) of large products requiring highpressure in a range of 500 to 1000 tons or more over a mold area of 50square feet or more.

BACKGROUND OF THE INVENTION

In the typical RIM operation, a mold cavity formed by at least twomating mold parts is filled with reactive chemicals that are mixed andinjected at high pressure into the mold cavity, wherein an exothermicpolymerization reaction substantially increases the pressure within thecavity. During the reaction process, it is important to clamp the moldparts firmly together to prevent the material being molded from escapingat the junctures between the mold parts. The RIM of large productsrequires tremendous compression forces over a comparatively large area,such that conventional presses used for high tonnage RIM operations tendto warp or deform during the molding process. Although the press bedsbetween which comparatively large mold parts are pressed comprise heavyrigid steel structures, it has not been economically feasible to providesuch presses that will not deform. In consequence, the force applied toclamp the mold parts together is distributed unevenly over the area ofthe mold, enabling the extrusion of pressurized reacting chemicalsthrough tiny spacings at the mold junctures. Such spacings on the orderof a thousandth of an inch are significant, may result in improperlyformed molded products, and in any event necessitate an additionaloperation to remove flash from the molded product.

Some RIM molds are characterized by a female mold part having a deepcavity that cooperates with a male mold part having projections thatextend deeply, i.e., as much as 30 inches or more, into the cavity whenthe mold parts are brought together to interfit at a mold closedposition. The mold cavity is usually defined by highly polished andaccurately machined surfaces. Accordingly, not only must the juncturesbetween the mold parts at their parting surfaces be tightly sealedduring the high pressure molding process, but each part of such moldsmust be orientated precisely with respect to a common reference plane,which is usually horizontal when the mold parts move vertically betweentheir open and closed mold positions. If the supporting structure foreither mold part becomes tilted slightly from the reference plane, theprojections of the male mold part that extend deeply into the femalecavity might contact and damage the mold and in any event, will alterand possibly cause a defective molded part. It is accordingly essentialto successful operation with such RIM molds that the supports for themold remain precisely parallel to the reference plane as the mold partsapproach the mold closed position.

Although the prior art relating to molding presses is extensive, verylittle of that art known to applicant is concerned with the problem ofpreventing or compensating for deformation of the press components. Thepatent to Hammon, U.S. Pat. No. 4,304,540, is typical of a conventionaltype of press that ignores the deformation problem and is thus limitedto the molding of small products involving comparatively low pressureapplications. The Hammon press is concerned with the SCM industry (sheetmoulding compounds) wherein extrusion of fluid high pressure chemicalsfrom the mold seams is not an important problem. In the SCM operation,material such as a sheet or blank to be formed is placed on a lower opendie part and thereafter shaped by a high tonnage forming operation thatrequires several inches of relative travel of upper and lower die partstoward each other.

Hammon provides stress or clamping rods 18 mounted at the corners offixed and movable press beds or mold supports 12 and 24 respectively. Alocking assembly 22 carried by the movable bed 24 clamps the serrations21 of each rod 18 to lock the movable bed 24 adjacent to a forming or"reference" position prior to application of the high tonnage formingpressure. Thereafter pressure is applied to the upper sides of pistons57, FIG. 1, which are secured to the rod 18 to pull the latter and bed24 downwardly in a forming operation. After the forming operation,pressure is applied to the lower ends of pistons 57 to effect astripping action by pushing the rods 18 upwardly.

Such a press is suitable for use only with comparatively small moldsbecause under extremely high tonnage force, in addition to deformationof other press components, the locking rods 18 are stretched, usuallynon-uniformly. Although the corner portions of the beds 12 and 24 aretightly clamped together, their central portions, when subjected to thehigh tonnage molding conditions of a RIM process, are insufficientlyclamped to the extent that the high pressure reactive chemicals beingmolded extrude from the mold as flashing.

The patents to Quere et al, U.S. Pat. No. 2,916,768 and Larso et al,U.S. Pat. No. 4,318,682, recognize the problem of deformation and thepossibility of improperly aligned press components. Quere '768, forexample, provides for independent adjustment of the corner mountedstress rods 5 and for the use of different pressures in the actuatingcylinders 3 to compensate for such deformation. Such a mold requiressophisticated controls and at best can only minimize deformation whenthe press is used with comparatively small molds. Even if the clampingforces at the corners of the mold are equalized, the mold will still besubject to the disadvantages of the corner mounted clamping devices usedby Hammon.

The Larson et al patent makes an attempt to compensate for deformationof press components by distributing the high pressure cylinders 38 overthe area of the mold. The patent also discloses the use of replaceablespacer shims 66 engageable with stop 64 to predetermine the spacingbetween the fixed support 18 and movable platen 16 at its lowermostposition, whereby the locking plates 80, 80' properly engage one of theslots in 60. However the structures disclosed are inadequate for RIMapplications and are unrelated to the concept of the invention disclosedherein.

Typically, of SMC presses, the lowermost position of Larson's platen 16is not comparable to the closed position of a RIM type press. Instead,it is equivalent to Hammon's "reference" position wherein the movableplaten is locked in a position that determines the start of the hightonnage forming operation. The high tonnage platen must then moveseveral inches at high pressure beyond the "reference" position to formthe sheet or plate between the dies, column 3, lines 30-34 of Larson etal.

Larson's upper platen 16 in effect becomes a fixed platen after it ismoved to and locked at its "reference" or lowermost position whichdetermines the beginning of the sheet forming operation. High tonnageforce and appreciable hydraulic power must then be applied by thecylinders 38 to move the lower platen 14 upwardly in a forming operationagainst the fixed platen 16. The mold parts of a RIM press on the otherhand are moved by comparatively low power means to a closed position incontact with each other. Thereafter, high tonnage force is only requiredto hold the mold closed sufficiently tightly during the moldingoperation to prevent extrusion of the pressurized chemicals from withinthe mold. Inasmuch as the mold in a RIM operation is already closed whenthe high tonnage pressure is applied, only a minuscule amount of highpressure hydraulic fluid is required to hold the mold closed.

Another type of press known to the art and concerned with the provisionof a uniform distribution of molding force over the area of a mold isvariously known as a bladder or pillow type press. Such presses providea high pressure chamber having a movable and usually deformable wallcoextensive with a movable mold plate and deformable against the latterto clamp it toward a fixed mold plate during a molding operation.Typically, high speed means are also provided for moving the movableplate and high pressure chamber in unison to and from a mold closedposition whereat the movable mold plate is adjacent to the fixed moldplate and in position to carry out the molding operation upon theinjection of pressurized fluid into the high pressure chamber. Suchpresses are only suitable for molding products having comparativelysmall surface areas requiring a comparatively small total molding force,wherein deformation of the press components is not a problem and highpressure stripping is not required. The deformable wall of the highpressure chamber can only exert a unidirectional molding force and isthus not suitable for high pressure stripping.

A typical pillow or bladder type press is disclosed in the Descrovi etal U.S. Pat. No. 4,247,278, which recognizes the problem of deformationof the mold plates and provides a fluid pressurized cylinder 77 havingan axial end wall 76, FIGS. 1, 2, or 216, FIGS. 3, 4, sufficiently thinand flexible to conform to deformation of an adjacent mold plate whenthe cylinder 77 is pressurized during a molding operation. Descrovi etal, like other pillow or bladder type patents, is not suitable for hightonnage operation. At the outset, it does not enable high pressurestripping by the same pressure exerting system that provides the moldclosing pressure. Also, the area of the deformable walls 76 and 216 mustbe strictly limited. Otherwise these walls will be ruptured if subjectedto the high pressure RIM of a large product. The deformable wall must besufficiently thin to conform to deflection of the adjacent mold carrierand must be sufficiently thick to prevent its destruction withincylinder 77. Accordingly bladder or pillow type presses such as Descroviet al must be operated within a comparatively limited range of clampingpressure.

SUMMARY OF THE INVENTION

The present invention is concerned with the problems resulting from thedistortion of press components during high tonnage RIM operationsinvolving large molds and provides an effective combination andarrangement of press components including a pair of mold supportingplatens movable with respect to each other to a mold closed position forclamping a composite mold or die therebetween, as for example a multiplepart mold for RIM, and also including an improved arrangement of sensorsand transducers that materially simplify the press operation and reducethe cycle time of repetitive operations.

In a preferred construction, a movable platen carried by a heavy andsturdy movable bolster or carrier is rapidly moved by a high speed andcomparatively low power hydraulic mechanism from an open mold positionto a closed mold position confronting a fixed platen supported by aheavy and sturdy fixed base. At the mold closed position, the twoplatens are confined between the movable carrier and fixed base, andcooperating mold parts confined between and supported by the two platensinterfit conventionally along parting surfaces to define a closed moldcavity therebetween. The fixed base also supports several guide pillarsand locking rods that extend slidably through the carrier in thedirection of its movement. The pillars guide movement of the carrier toand from the open and closed mold positions. The locking rods provide aplurality of closely and uniformly spaced annular locking grooves orserrations selectively engagable with locking dogs mounted on thecarrier to lock the latter at incremental positions against movementwith respect to the fixed base and platen.

Depending upon the dimensions of the cooperating mold parts between theplatens at the mold closed position, the locking dogs mounted on thecarrier may not be properly aligned with the serrations of the lockingrods to lock therewith when the carrier moves initially to the closedmold position. In order to lock the carrier positively with respect tothe fixed base, it may be necessary to move the carrier and locking dogscarried thereby a fraction of the incremental spacing between successiveserrations of the locking rods. To this end, when the carrier stops atthe closed mold position, a transducer and sensor carried by the fixedbase and carrier cooperate to determine the distance "Y" that thecarrier must be moved from the closed mold position to the nextsuccessive locking position, and also to initiate a sequence of pressoperations as follows:

(1) The low power hydraulic mechanism is activated to move the carrierindependently of the movable platen from the closed position to the nextsuccessive locking position, i.e., the distance "Y" determined by thesensor. During this sensor determined movement of the carrier to alocking position, the movable and fixed platens remain at the moldclosed position. In consequence, a space equal to the sensor determineddistance "Y" is created between the carrier and the movable platen.

(2) The locking dogs and a spacer mechanism are then actuated, whereuponthe locking dogs engage the aligned serrations of the locking rods andlock the carrier against further movement. Essentially simultaneously,the spacer mechanism moves a spacer into position to span the space "Y"created between the carrier and the movable platen.

(3) Thereafter, a high tonnage force exerting mechanism mounted on thelocked carrier forces the movable platen against the fixed platen,thereby to seal the parting surfaces between the mold parts.

(4) The RIM apparatus is then actuated to inject the reactive chemicalsinto the sealed mold cavity in a conventional manner.

(5) Upon completion of the molding operation, the carrier is unlockedand returned with the movable platen to the initial mold open positionby the high speed hydraulic apparatus to enable repetition of the cycle.

The spacer inserted by the spacer mechanism between the carrier and themovable platen remains in place until it is removed at the election ofthe press operator, as for example to accommodate a mold of a differentdimension. Thus, during successive molding cycles, when the carriermoves the movable platen to the mold closed position, the carrier willalready be spaced from the movable platen by the aforesaid sensordetermined distance, such that the locking dogs will be properly alignedwith the locking rods for immediately locking the carrier againstmovement during the RIM operation. Operation of the press is thusmaterially simplified and the cycle time for repetitive moldingoperations is appreciably shortened.

The high tonnage force exerting means preferably comprise a plurality ofhigh pressure piston-cylinder assemblies mounted on the carrier andhaving their piston rods or connectors separately extensibleindependently of each other in the direction from the carrier toward themovable platen and connected thereto at a corresponding plurality ofseparate locations confined within the area of the mold that is clampedbetween the two platens. The connectors are arranged so that when theyare extended, each independently of the others, they force the movableplaten against the fixed platen at the closed mold position.

In the event that some of the press components tend to deform during ahigh tonnage clamping operation, such that the junctures between themold parts clamped between the platens are not tightly sealed, theindependently extensible connector connected to the movable platenadjacent to any unsealed juncture will continue its clamping movementuntil the junctures between the parting surfaces of the mold parts arecompletely sealed.

The locking rods when engaged by the locking dogs sustain the entirereaction force of a high tonnage clamping operation, such that the guiderods are unaffected by the clamping operation and their function inguiding movement of the carrier is not hampered. Also the guide andlocking rods are located outwardly of the area of the platens, such thatthe mechanism for operating the locking dogs may also be located outsideof that area. Thus the force exerting means, preferably high pressurecylinders, may be mounted on the carrier as closely together as desiredwithin that area.

Also preferably a pair of locking dogs associated with each locking rodare slidably supported on the carrier for moving simultaneously inopposite directions to and from positions of locking engagement with thelocking rod. A first spring interposed between fixed portions of thecarrier and one of the dogs of said pair yielding urges the one dog toits position of locking engagement. A second spring interposed betweenfixed portions of the carrier and the other dog of said pair yieldinglyurges the other dog to its position of locking engagement. A pair offorce exerting members connected respectively with the dogs are movablesimultaneously in said opposite directions to move the dogssimultaneously to their positions of locking engagement against thereaction of the springs. Also preferably a pair of spacers are providedfor engaging portions of each dog and the carrier for blocking unlockingmovement of the dogs at a predetermined limiting position.

The locking dogs slidable on the carrier are necessarily substantial insize and weight in order to withstand the high tonnage clamping forcewhen interlocked with the locking rods. As a result, appreciable slidingfriction would ordinarily exist between the locking dogs and carrierwhen the dogs are moved to and from locking engagement with the lockingrods. In order to reduce such sliding friction, a resilient device isinterposed between the carrier and dogs to elevate the latter yieldinglytwo or three thousandths of an inch from the carrier. The annulargrooves of the locking rods also provide approximately an eighth of aninch clearance for the locking dogs, such that the elevated dogs arefreely received within the grooves when aligned for locking engagementtherewith. During high tonnage clamping, the clamping force readilyoverrides the resilient device and eliminates any clearance between thedogs and carrier.

The preferred high pressure cylinder and piston assemblies describedherein also provide compact and readily controlled reversible means foreffecting high pressure stripping where such is required, utilizing thesame pressure source required for the high tonnage clamping. Howeverother force exerting assemblies known to the art, such as toggle orelectro-mechanical assemblies by way of example may be substituted forthe high pressure cylinder-piston assemblies. Also, although the presentinvention is described herein in application with high tonnage RIM oflarge products, such as polyurethane parts and the like, the pressdescribed may be used in other applications where a plurality ofindependently extensible force exerting connecting rods are required toapply force at a corresponding plurality of separate closely spacedlocations within the area of a mold.

Other advantages and applications of the present invention will beapparent from the following description and appended claims, referencebeing had to the accompanying drawings forming a part of thisspecification wherein like reference characters designate correspondingparts in the several views.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevational view of RIM press embodying thepresent invention, showing the press at its mold open position, as forexample at the beginning of a molding cycle.

FIG. 1A is a fragmentary schematic view illustrating the relationbetween the locking rods and dogs associated with the FIG. 1 position.

FIG. 1B is a schematic representation of the press control centercomprising the interacting hydraulic and sensor systems.

FIGS. 2 and 2A are similar to FIGS. 1 and 1A, but show the presselements at the initial mold closed position.

FIGS. 3 and 3A are views similar to FIGS. 1 and 1A, showing the presscomponents after the carrier has been moved to the locking position andprior to activation of the spacer mechanism.

FIGS. 4 and 4A are views similar to FIGS. 1 and 1A, showing the spacermechanism in position to assure that the carrier will always be at theFIG. 3 locking position during repetitive molding operations when themold parts are at their closed position.

FIG. 5 is an enlarged fragmentary view similar to FIG. 4 showing detailsof the spacer mechanism.

FIG. 6 is a schematic plan view of the press.

FIGS. 7 and 8 are plane views of the locking mechanism, showing thelatter in the unlocked and locked position respectively.

FIG. 9 is a fragmentary elevation of FIG. 8, showing details of theresilient device for elevating the locking dogs to reduce frictionduring movement to and from their locking positions.

It is to be understood that the invention is not limited in itsapplication to the specific details described herein, since theinvention is capable of other embodiments and of being practiced orcarried out in various ways, and that the phraseology or terminologyemployed herein is for the purpose of describing the invention claimedin the appended claims.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION:

Referring to the drawings, a high pressure press for reaction injectionmolding (RIM) on the order of 500 to 1000 tons or more capacity isillustrated comprising in the present instance a rigid fixed base 10supporting and secured to a lower fixed mold platen 11. A lower fixedmold part 12 is supported and conventionally secured to the platen 11. Amovable carrier or bolster 13 of rigid material is provided withelongated sleeve bushings 14 that ride along four guide pillars 15extending vertically from mountings on the base 10 adjacent to itscorners and outwardly of the platen 11. A pair of comparatively highspeed hydraulic assemblies including cylinders 16 mounted on the midlineof the base 10 engage endwise extensions of the carrier 13 for rapidlymoving the latter along the guides 15 between an elevated open position,FIG. 1, and a lower closed position, FIGS. 2, 3, and 4, as describedbelow.

Mounted on the upper surface of the carrier 13 are a plurality of highpressure hydraulic cylinders 17, eight in the present instance, FIG. 6.Each cylinder 17 contains a bidirectionally operated piston 18 connectedwith a vertically movable connecting rod or connector 19 that extends insliding sealing relationship through the lower end of the associatedcylinder 17 and freely through the carrier 13 to a connection 20 at itslower end with a movable upper platen 21 for supporting the latter andurging it vertically in high pressure clamping, and stripping operationswhen required, upon actuation of the pistons 18. The platen 21 of rigidmaterial is essentially coextensive with the underlying platen 11. Anupper movable mold part 22, conventionally secured to the platen 21overlies and cooperates with the lower mold part 12 at the closedposition of the press, FIG. 2, to define a mold cavity 23 therebetween,which necessarily must be sealed during a molding operation. By virtureof the press structure described, including the cylinders 17 mountedabove the carrier 13, the bushings 15 may be elongated appreciably toprovide the desired support for the carrier 13 on the pillar 14.

Also mounted on the base 10 adjacent to and slightly inwardly of theguide pillars 15 respectively, FIG. 6, are four vertical locking rods 24that extend freely through the carrier 13 and provide uniformly spacedannular grooves or serrations 25 throughout their upper portions, FIGS.1A to 4A. The parts described thus far may be formed from sturdystructural steel alloys. The cylinders 16 and 17 are connected in anoperative hydraulic circuit, schematically illustrated in FIG. 1B andboth may be operated by the same source of high pressure hydraulicfluid.

Associated with each rod 24 is a locking mechanism comprising a pair oflocking dogs 26a, 26b, FIGS. 7 and 8, mounted on the upper surface ofcarrier 13 for horizontal movement toward and from opposite sides of theassociated rod 24. The dogs 26a,b are provided with semicylindricalrecesses 27 serrated at 28 to mate and interlock with the associatedrods 24, FIG. 8. Movement of each pair of dogs 26a,b to and from thelocking position is accomplished by an associated spring assistedhydraulic mechanism indicated generally at 29 and comprising ahorizontally movable hydraulic cylinder 30. The latter is closed at itsouter end and secured thereat integrally to a horizontal transverse bar31. The cylinder 30 is also closed at its inner end and secured thereatintegrally to a guide 32 for a piston rod 33 connected to a piston 34reciprocable within the cylinder 30. The rod 33 extends horizontallyfrom the piston 34 and perpendicularly to both the transverse bar 31 andthe associated rod 24 and also slideably through the guide 32 in sealingrelationship to a connection 35 at its inner end with the adjacent dog26a.

A pair of rods 36 parallel to the rod 33 are connected with the otherdog 26b at opposite sides of the rod 24 and extend outwardly in guidedsliding relationship through the dog 26a and a pair of fixed guides 37respectively and then to screw threaded ends secured to the oppositeends of the bar 31 by nuts 39. The guides 37 are secured to the carrier13. Extending around the rods 36 are a pair of helical springs 40,compressible between the dog 26a and fixed guides 37, and a second pairof helical springs 41 compressible between the guides 37 and bar 31. Thepiston-cylinder assembly 29 is selectively operated by hydrauliccircuitry for applying hydraulic pressure to either the left or rightface of piston 34.

When pressure is applied to the left face of piston 34, the latter ismoved to the FIG. 7 position at the limit of its rightward movementwithin cylinder 30, thereby to move the dog 26a rightward to the FIG. 7position and out of engagement with the rod 24. Simultaneously thecylinder 30 and connected bars 31 and 32 are moved leftward, thereby tomove the rods 36 leftward and to force the dog 26b leftward out ofengagement with the rod 24, FIG. 7. The simultaneous rightward movementof dog 26a and leftward movement of bar 31 compresses the springs 40 and41 respectively between the dog 26a and guides 37 and between guides 37and bar 31. Thus each dog 26a and 26b moves away from the locking rod 24to the FIG. 7 unlocked position by an amount equal to one-half the totalstroke or relative movement between the piston 34 and its cylinder 30,i.e., the piston 34 and cylinder 30 each move a half stroke in oppositedirections relative to the fixed supports 37.

In order to assure the half stroke movement of the cylinder 30 andpiston 34, a pair of tubular spacers 42 and 43 of equal lengths encloserespectively each pair of springs 40 and 41 and are located respectivelybetween the guides 37 and dog 26a and between the guides 37 and bar 31.The tubular spacers 42 and 43 closely space the fixed guides 37 equaldistances from the adjacent portions of the dog 26a and bar 31 when themechanism 29 is at the FIG. 7 unlocked position. At the FIG. 6 lockedposition, the spacers 42, 43 float on their respective springs 40, 41.

Upon application of pressure to the right face of piston 34, orpreferably upon release of pressure within cylinder 30, the compressedsprings 40 move the dog 26a leftward to the locked position, FIG. 8, andthe compressed springs 41 move the bar 31 and connected dog 26brightward to the locked position, whereat the interfitting serrations25, 28 of the rod 24 and dogs 26a,b lock the carrier 13 against movementlongitudinally of the rod 24. The locking mechanism described is failsafe in the event of loss of pressure. In addition to the guides 37secured to the carrier 13, a pair of fixed guides 44 secured to thecarrier 13 in parallelism with the rods 36 engage opposite sides of thedogs 26a,b in sliding guided relationship to enable their horizontalmovements to and from their locking positions as described.

Vertical movement of the dogs 26a,b independently of the carrier 13 islimited by a plate 45 that overlies and is secured to the fixed guides44. The locking rod 24 passes freely through an opening in the plate 45,and the plate 45 overlies the dogs 26a,b with a small verticalclearance, such that the dogs slide between the guides 44 to which theplate 45 is secured. The vertical dimension of each dog 26a,b will beseven or eight inches for a 1000 ton press in order to provide thestrength to withstand the high tonnage clamping force in the lockedposition. Accordingly a second pair of rods 36 and similar associatedstructure preferably overlie the rods 36, FIG. 9.

In order to minimize the sliding friction and resulting wear between thecarrier 13 and dogs 26a,b when the latter are moved to and from lockingengagement with the rod 24, the weight of the dogs 26a,b in eachmechanism 29 is supported by a pair of helical springs 64 seated withina pair of recesses 65 in the plate 45 and coiled around a pair of largeheaded bearing support screws 66, FIG. 9. Each screw 66 extendsvertically downward from the associated recess 65 and slidable throughthe plate 45 to a screw connection at its lower threaded end with abearing block 67. The latter contains a horizontal cylindrical sleevebearing 68 for a pin 69 slidable coaxially within the bearing 68. Athreaded end 69a of the pin 69 screws into the adjacent dog 26b at alocation essentially in coaxial alignment with the uppermost rod 36 andis thus secured to the dog 26b for movement therewith to and from thelocking position. During such movement, the pin 69 slides coaxiallywithin the bearing 68. The dog 26b is recessed at 70 to accommodate thebearing block 67 when the dog 26b is moved out of contact with the rod24, FIG. 7.

The spring 64 is under compression between the base of the recess 65 andthe enlarged head of the screw 66 and normally holds the pin 66 andconnected block 67 and dog 26b upwardly to the extent of a fewthousandths of an inch clearance between the upper surface of the block67 and the overlying cover plate 45. By reason of the rods 36 connectedto the dog 26b and extending through the dog 26a, the latter is alsoelevated, such that both dogs 26a,b normally clear the upper surface ofthe carrier 13 by a few thousandths of an inch. To this end, thesupports 37 permit sufficient vertical movement of the rods 36 to enablethe resiliently induced clearance between the dogs 26a,b and carrier 13.Likewise, approximately an eighth of an inch clearance is provided forthe projections of the serrated dogs 26a,b within the mating annulargrooves of the serrated rods 24. When the press is in the high tonnageclamping mode, the clamping force overrides the springs 64 and the dogs26a,b seat solidly on the carrier 13.

In accordance with a typical operation of the RIM press, starting by wayof example from an elevated or mold open position of the carrier 13,FIG. 1, with the pistons 46 and rods 47 of the cylinders 16 extendedessentially to their limits of upward movement, the dogs 26a,binterlocked with the locking rods 24, FIG. 1A, and the pistons 18retracted upwardly to support the movable platen 21 at its upper limitof movement against the carrier 13, the locking assemblies 29 may thenbe operated as described to release the dogs 26a,b from the serratedrods 24. The hydraulic fluid pressure within cylinders 16 is suitablycontrolled by hydraulic circuits, FIG. 1B, to effect rapid downwardmovement of the heavy carrier 13 and platen 21 toward the closedposition, FIG. 2. Shortly before the carrier 13 reaches the FIG. 2closed position, whereat the mold parts 12 and 22 interfit with eachother in mating relationship to define a closed mold cavity 23, the rateof descent is retarded to allow the mold parts 12, 22 to come togethergently. The initial closing movement of the carrier 13 may be controlledeither manually or by the sensing system described below.

Inasmuch as the mating mold parts 12, 22 may be replaced by other moldparts of different sizes for different molding operations, the serratedrods 24 at the initial closed position may not interfit with theserrated dogs 26a,b, FIG. 2A. Accordingly, before actuation of thelocking mechanisms 29, the carrier 13 must be raised to the nextsuccessive locking position, FIGS. 3, 3A, whereat the dogs 26a,binterfit in locking engagement with the rods 24. During this operation,the platen 21 and mold part 22 will remain at the closed FIG. 2position. In consequence, a space 48 will be created between the carrier13 and platen 21 amounting usually to less than an inch, but not morethan the spacing between successive locking positions.

In order to move the carrier 13 precisely and rapidly to the FIG. 3locking position, a pair of linear displacement transducers 49 aresupported by the base 10 in parallelism with the locking rods 24 and onthe midline of the press adjacent to its opposite ends. Each transducer49 is associated with a sensor 50 mounted on the carrier 13. Each sensor50 and associated transducer 49 may be conventional and connected in anoperative sensing circuit 72 cooperable with the hydraulic circuit 71 toenable the sensor 50 to determine and control its position along thelength of the transducer 49.

The locking rods 24 are accurately adjusted on the base 10 so that eachlocking mechanism 29 will engage and lock with its associated rod 24 atprecisely the same distance from the base 10 when the carrier 13 is atthe FIG. 1 open position. As a result, the carrier 13 at the openposition will be perfectly parallel with the base 10. When thecircuitry, FIG. 1B, is activated to initiate downward movement of thecarrier 13 toward the FIG. 2 closed position, the sensors 50 incooperation with the transducers 49 will sense their positions along thelength of their associated transducers 49 to assure that opposite endsof the carrier 13 are always equidistant from the base 10.

If one of the sensors 50 should detect that it is a trifle lower thanthe other, the hydraulic system 16 associated with the lower sensor 50will reduce the rate of downward movement of the lower end of thecarrier 13. In consequence, equal distances of both sensors 50 from ahorizontal reference plane, i.e., the horizontal base 10, is maintainedwithin an accuracy of a thousandth of an inch and the desired attitudeor horizontal orientation of the carrier 13 is assured throughout itsmovement to the closed position.

When the carrier 13 approaches the FIG. 2 closed position, the sensors50 sense that condition and signal the hydraulic circuit 71 to retardthe rate of downward travel of the carrier 13. When the movable moldpart 22 finally seats on the fixed mold part 12 at the interfittingclosed position, downward movement of the carrier 13 stops, and thehydraulic circuit signals the sensors 50 to determine the distance "Y",FIG. 2A, that the carrier 13 must be raised to a locking position, FIG.3A, whereat the dogs 26a,b can interlock with the rods 24. Successivelocking positions are spaced vertically along the locking rod byincrements on the order of magnitude of about one to one and a quarterinch. The distance "Y" will be a fraction of such an increment.

The sensor 50 in cooperation with the transducer 49 immediately sensesthe distance "Y" and initiates a sequence of signals whereby thehydraulic circuit associated with cylinders 17 enables pistons 17 tofloat and cylinder 16 is actuated to elevate the carrier 13 an amountequal to the distance "Y" whereat the projections of the dogs 26a,balign centrally with the grooves of the rods 24 with approximately aneighth inch clearance. As soon as the carrier 13 is raised the distance"Y" to the next successive locking position, the locking mechanisms 29are activated to move the dogs 26a,b into locking engagement with therods 24. Essentially simultaneously, a spacer mechanism is activated tofill the space 48, amounting to the distance "Y", between the carrier 13and movable platen 21, as described below.

As soon as the carrier 13 is locked against movement by the mechanism29, the high pressure cylinders 17 are actuated to force the pistons 18and connecting rods 19 downward against the platen 21, thereby to clampthe mold parts 12, 22 together and effect a sealed mold cavity 23therebetween, whereupon a conventional RIM mix head 51, FIG. 1, isactuated to discharge reactive chemicals at high pressure into thecavity 23 to enable completion of the RIM operation as is conventional.Inasmuch as the mold parts 12, 22 are in contact at their mold closedposition, the high tonnage clamping force is only applied to effectivelyseal the junctures between the mold parts 12, 22. The travel of thepistons 18 and connecting rods 19 will thus be miniscule, i.e.,primarily as required to compensate for unavoidable warpage of the presscomponents, and the hydraulic power required for the high tonnageclamping force will be nominal.

In the present instance the spacer mechanism comprises six rotatablespindles 52 driven by torque limiting sprockets 53 and sprocket chain54, FIGS. 5 and 6. The chain 54 in turn is driven by motor 55 through aspeed reducer 56. As illustrated in FIG. 6, the chain 54 extendscontinuously around the six sprockets 53 and suitable idle rollers. Eachsprocket 53 is keyed at 57 to a spindle 52 to rotate the same. Eachspindle 52 extends vertically and rotatably through a flange 13a of thecarrier 13 to a lower longitudinally splined end 58. A cylindricalspacer 59 is splined on the end 58 to rotate with the spindle 52 andalso to move axially along the spline. The upper portion of the spacer59 has a reduced diameter externally threaded portion in screw threadedengagement with an internally threaded non-rotatable portion of carrier13 or sleeve 61 secured within a lower flange 13b of the carrier 13.

Upon rotation of the spindle 52, the spacer 59 splined thereto alsorotates and is driven downward by the screw threaded engagement withsleeve 61 until the enlarged lower end of the spacer 59 strikes theupper surface of platen 21 and actuates a proximity switch 62 securedwithin the platen 21. By reason of a torque limiting coupling betweenthe sprocket 53 and spindle 52, the spacer 59 and spindle 52 stoprotating. When the proximity switches 62 associated with all six of thespacers 59 have been actuated, a signal is sent to stop motor 55.

During subsequent molding operations, when the press is actuated to movethe carrier 13 and movable platen 21 to the closed FIG. 2 position fromthe open FIG. 1 position, the carrier 13 will already be at a lockingposition. Accordingly, the process of sensing the distance "Y", raisingthe carrier 13 to the next successive locking position, and actuation ofthe above described spacer mechanism will be eliminated. The sensor 50will recognize that the distance "Y" equals zero and will immediatelycause the control center 71, 72 to actuate the locking mechanism 29 tolock the carrier 13 against further movement, then initiate the hightonnage clamping operation of cylinders 17, and thereafter initiateoperation of the mix head 51 to inject the pressurized reactivechemicals into the mold cavity 23.

Upon completion of the RIM, the carrier 13 is unlocked from the rods 24and the high pressure differential across the pistons 18 may be reversedto effect high tonnage stripping, where required, to move the platen 21slightly upwardly to strip the mold part 22 from the molded productwithin the mold cavity 23. Usually, the stripping force is less than the1000 ton molding force, as for example in the neighborhood of 200 tons.Preferably, when high stripping force is not required, as for examplewhen less than 200 tons, the rods 24 may be unlocked from the dogs 26a,bafter the RIM operation and the cylinders 16 will be activated to effectthe stripping. The stripping and subsequent return of the carrier 13 tothe FIG. 1 open position will be under the above described sensorcontrol to maintain the horizontal attitude of the carrier as requiredto prevent damage to a mold having a deep mold cavity. Uniform andsimultaneous stripping movement of all parts of the plate 21 is thusfacilitated because it is easier to control the stripping operation andhigh speed movement of the carrier 13 between the open and closedpositions by means of the two cylinders 16 than the eight or morecylinder 17.

As noted above, a major problem confronted by high tonnage RIM pressesresults from deformation of the press components during the highpressure clamping force required to overcome the reaction pressure ofthe molding products. The present invention mounts the high tonnagepressure exerting cylinders 17 on the carrier 13 at preselectedlocations spaced within an area coextensive with the area of the mold23, FIG. 6, such that at least some of the connectors 19 engage theplaten 21 within that area. The connectors 19 are forced independentlyof each other against the platen 21 by the high pressure fluid withinthe cylinders 17. Thus any localized unsealed juncture between the moldparts 12, 22 resulting from deformation of the press components, such asbowing of the carrier 13 and base 10, or relative cocking therebetweenresulting from the clamping force on the corner mounted locking rods 24,or their non-uniform stretching, and from pressure within the mold 23,will be closed by additional downward movement of the connecting rod 19overlying the unsealed juncture.

The high tonnage downward extension of each rod 19 continues until allthe junctures between the mold parts 12, 22 are compacted firmlytogether and sealed. The mold parts 12, 22 are necessarily sufficientlystrong to resist being crushed by the forces exerted by the highpressure assemblies 17, 18, 19, which forces may amount to approximately125 tons at each location 54 when the force of a 1000 ton press isdistributed among eight rods 19. The condition whereat the mold parts12, 22 are pressed together sufficiently to positively seal the moldcavity 23 determines the limit of downward movement of the connectingrods 19. The pressure within the cylinders 17 is then maintained to holdthe mold cavity 23 closed until completion of the molding reaction,whereupon the press components are returned to the starting position.

The press may operate at pressures in the cylinders 17 on the order ofmagnitude of 2500 psi for example, wherein the plan area of the moldparts 12, 20, FIG. 6, may be on the order of magnitude of 6 feet by 9feet by way of example. The spacing between the connections 20 of theconnectors 19 with the platen 21 will be determined by the rigidity ofthe platen 21, but in any event will be sufficiently small so that theleverage of localized deforming forces exerted on the mold platens 11and 21 between the locations 20 will be too small to enable significantdeformation of these plates between adjacent regions 20. It isaccordingly apparent that the independently extensible connectors 19 notonly compensate for deformation of the press components, they mayactually suppress deformation by preventing initial buckling of suchparts as the platens 11 and 21. Even when the four locking rods 24 donot stretch identically, or in the event of slight deformation of theheavy base 10, the action of the independently extensible rods 19described above will maintain the mold 23 closed and sealed throughoutthe molding operation.

The specific hydraulic sensor and electrical circuitry associated withthe cylinders 16, 17 and 30, sensors 49, 50 and 62, and motor 55required to operate the press mechanism as described, forms no part ofthis invention because such elements and their operation and control arewell known to the art. Accordingly, the hydraulic circuitry or system71, including proportionate flow control valves for maintaining thecontrolled horizontal descent of the carrier 13 to the FIG. mold closedposition, and computer and sensor center 72 interconnected at 73 fortransmission of operating signals therebetween is illustratedschematically in FIG. 1B, wherein 74 schematically represents thehydraulic conduits operatively connecting cylinders 16, 17, 30 withtheir hydraulic sources and 75 schematically represents the circuitsoperatively connecting sensors 49, 50, 62 and motor 55 with their powersources and computer control for effecting the operating sequencesdescribed above.

I claim:
 1. A press having a fixed base, a locking rod mounted on saidbase, said rod having a plurality of annular serrations spaced along itslength, a carrier movable along said rod, and means for locking saidcarrier against movement along said rod comprising a pair of lockingdogs mounted on said carrier for moving to and from locking engagementwith opposite sides of said rod, said dogs having serrated recesses forreceiving said opposite sides and mating at said locking engagement withthe serrations of said rod, first spring means interposed betweenportions fixed respectively to said carrier and to one of said dogs foryieldingly urging said one dog to its locking engagement, second springmeans interposed between portions fixed respectively to said carrier andto the other of said dogs for yieldingly urging said other dog to itslocking engagement, and a pair of force exerting means movablesimultaneously with respect to each other in opposite directions andconnected with said dogs respectively for moving the lattersimultaneously from their positions of locking engagement against thereaction of said first and second spring means.
 2. The combinationaccording to claim 1 and means for blocking movement of each dog at apredetermined limit of movement from its locking engagement comprising apair of spacers, one of said spacers being arranged for engagingportions fixed respectively to said carrier and to said one dog when thelatter is at its said predetermined limit of movement, the other of saidspacers being arranged for engaging portions fixed respectively to saidcarrier and to said other dog when the latter is at its saidpredetermined limit of movement.
 3. The combination according to claim1, said pair of force exerting means comprising a piston member and acylinder member in a fluid actuated piston-cylinder assembly, a rodextending in the direction of movement of said dogs to and from theirlocking engagement and slideably through portions fixed respectively tosaid carrier and to said one dog, said rod having one end connected tosaid other dog and having a second end connected to a portion fixed toone of said members, said first and second spring means comprising firstand second coil springs respectively around said rod, said first springbeing interposed between portions fixed respectively to said carrier andto said one dog, said second spring being interposed between portionsfixed respectively to said carrier and to said one member.
 4. Thecombination according to claim 3, means for stopping movement of eachdog at a predetermined limit of movement from its locking engagementwith said rod comprising first and second tubular spacers around saidfirst and second coil springs respectively, said first spacer beingarranged for engaging portions fixed with respect to said carrier andsaid one dog when the latter is at its said predetermined limit ofmovement, said second spacer being arranged for engaging portions fixedwith respect to said carrier and to said other dog when the latter is atits said predetermined limit of movement.
 5. A press according to claim1, said rod extending vertically and said carrier being movable alongsaid rod, said dogs being movable horizontally on an upper surface ofsaid carrier, and means for yieldingly elevating said dogs from saidsurface to reduce frictional engagement therebetween upon movement ofsaid dogs to and from their locking engagement comprising a pair ofvertically spaced members associated with said carrier and one of saiddogs respectively, one of said members being mounted to movehorizontally in the direction of movement of said one dog, the memberassociated with said one dog being movable vertically and beingconnected to said one dog for moving the latter vertically therewith,means connecting said dogs for moving vertically in unison, resilientmeans interposed between said members for yieldingly urging said memberassociated with said one dog vertically into the vertical space betweensaid members, thereby to elevate said dogs from said surface.
 6. A pressaccording to claim 5 means securing said one member to said one dog formoving in unison therewith, a vertically movable bushing support, saidone member being slidably journaled in said bushing support, and theother member being fixed with respect to said carrier.